KR970000645B1 - Optical pick up - Google Patents

Abstract

The optical pick up system is comprised of a beam generating from a semiconductor laser(1) being irradiated in parallel with an active layer xy-plane of the semiconductor laser(1) so that the beam get to be P-polarized when being irradiated at PBS(polarized beam splitter)(4); a hologram(12) being comprised of a couple of H1, H2, semicircle-type holograms; 6-division optical detector(11) determining position of the hologram(12) for a couple of a semicircle-type beam connected together by a couple of the holograms to maintain a predetermined interval each other; the interval between a couple of the semicircle beams on the 6-division optical detector(11) being equal to line width for 6-division.

Description

Optical pickup system

1 is a block diagram of a conventional optical pickup system.

FIG. 2 is a detailed view of an eight-segment photodetector that envisions the optical pickup system of FIG.

FIG. 3 is a converging form of a three beam on a disk to illustrate FIG.

4 is a diagram showing the separation of S-wave P waves by an improved Wollastone prism for explaining FIG.

5 is a form of a five-beam focused on the eight-segment photodetector of FIG.

6 is a connection diagram of a beam that is changed on a light detector as a disc and an objective lens distance change in the optical pickup system of FIG. 1, and (a) is a beam focusing speed when there is no focus error. (b) and (c) are beam focusing speeds when a focus error occurs.

7 is a block diagram of the optical pickup system of the present invention.

8 is a block diagram of a hologram module constituting the optical pickup system of the present invention.

9 is an explanatory diagram of astigmatism by holograms for explaining the optical pickup system of the present invention.

10 is an explanatory diagram of laser beam diffraction by holograms for explaining the optical pickup system of the present invention.

11 is a focusing speed of a laser beam on a servo optical detector according to a change in the distance between an objective lens and a disk in the optical pickup system of the present invention, and (a) is a beam focusing speed when no focus error occurs. (b) is the beam focusing speed when the distance between the disk and the objective lens is close. (c) is the beam focusing speed when the distance between the disk and the objective lens is increased.

12 is a diagram illustrating separation of S and P waves by Wollastone prism constituting the optical pickup system of the present invention.

* Explanation of symbols for main parts of the drawings

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2: 3-beam diffraction grating

3: collimating lens 4: polarizing beam splitter

5: reflective mirror 6: objective lens

7: improved Wollastone prism 8: imaging lens

9: concave lens 10: 8 split photodetector

11: 6 split photodetector 12: 2 split hologram

13 module 14 focusing lens

15: two-part photodetector 16: actuator

17: Wollastone Prism

The present invention relates to an optical pickup system, and to provide an optical pickup system capable of solving problems such as a decrease in a reading speed and a manufacturing cost increase due to an increase in the number of parts and a weight increase due to a complicated structure of a conventional optical pickup system.

The conventional optical pickup apparatus includes a semiconductor laser 1 used as a light source as shown in FIG. 1, a diffraction grating 2 for making a sub beam for tracking error of an optical disc, A collimator lens 3 for converting the beam passing through the diffraction grating into parallel light, and a 50% reflectance of the S-polarized beam and a P-polarized beam polarized in a direction perpendicular thereto. Polarizing beam splitter (4), which reflects and transmits, and a reflective mirror (5) for bending a beam passing through the PBS in a direction of a disk, and parallel reflected on the disk by the reflective mirror. The beam emitted from the semiconductor laser proceeds in the order of the objective lens 6 for focusing the light, and the beam reflected by the disk is converted into parallel light again through the objective lens, so that the reflective mirror 5 and PBS 4 After passing through, S wave, P wave and S wave and P wave An incident light beam is incident on an improved Wollastone prism 7 that separates the incident beam into three beams, which are separated by the improved Wollastone prism, after passing through the imaging lens 8 and then focusing on a focus error. By the concave lens 9 having a toric surface for detection, it is configured to form an image in photodetectors 10 composed of eight divisions.

The operation of the conventional optical pickup device configured as described above will be described with reference to FIGS. 1 to 6.

The laser beam emitted from the semiconductor laser is diffracted by the diffraction grating 2 into a main beam and two sub beams, and these three beams are converted into parallel light by a collimator lens 3. And enters the PBS 4.

The three beams passing through the PBS are reflected by the reflective mirror 5 toward the disk and focused on the disk by the objective lens 6 as shown in FIG. 3 so that the main beam is used for information reading and focus error detection. The auxiliary beam of is used to detect a tracking error.

These three beams are reflected on the disk with information recorded on the disk (pit information or kerr rotation by the magnetization direction) and information necessary for tracking error detection, and as described above, the objective lens 6 and the reflecting mirror 5 And then into the improved Wollastone prism via the PBS (4).

The incident beam passes through the improved Wollastone prism and the main beam is divided into three beams of S-wave, P-wave, and S + P-wave according to the polarization, so that a total of five beams are formed as shown in FIG. Each of the five concave lenses 9 having an annular surface which is incident on (8) and increases the flared angle of the beams exiting the imaging lens and at the same time generates astigmatism in the main beam for focus error detection. The beam is focused on 8-segment photodectors 10 as shown in FIG.

The tracking error detection by the auxiliary beam is detected by the signal difference between e and f, i.e., the tracking error signal TES as shown in Equation 1 below, in the eight-segment photodetector by the three-beam detection method. As shown in the figure, as the distance between the optical disk and the objective lens changes, the signal difference due to the beam change in the eight-segmented light detectors a, b, c, and d due to astigmatism, that is, the focus error signal of Equation (2) FES).

TES (Tracking Error Signal) = Se-Sf

(Se and Sf are detection signals of 8-segment photodetector)

FES (Focus Error Signal) = (Sa + Sc)-(Sb + Sd)

Therefore, if no tracking focus error occurs, TES = 0, FES = 0. In the case of the magneto-optical signal (kerr rotation in the magnetization direction), the information read on the disk is detected by the signal difference of the eight-segment photodetector i.j, that is, the signal difference between the S wave and the P wave, that is, the following equation (3).

Optical information signal (photomagnetic signal) = Si-Sj

In the case of the uneven-shaped pit signal recorded on the compact disc, as shown in Equation (4), it is detected by the light quantity change of the eight-segment light detectors i and j.

Optical information signal (pit signal) = Si + Sj

However, such a conventional optical pickup system uses a diffraction grating to detect a docking error by a 3-beam method, an astigmatism method to detect a focus error, and reads information recorded on a magneto-optical disk. A concave lens with a toroidal surface that is difficult and expensive to manufacture and an improved Wollaston prism that is difficult to fabricate were used.

The conventional optical system has a disadvantage of increasing the cost of manufacturing as well as the reduction of the reading speed due to the increase in the weight of the optical pickup system itself by increasing the number of optical components.

Accordingly, an object of the present invention is to solve the above problems.

The object of the present invention is the collimation lens for converting the light generated from the semiconductor laser into parallel light, and the S-polarized beam of the parallel light of the beam generated from the semiconductor laser and the beam reflected on the optical disk is the total reflection, P-polarized beam of A polarizing beam splitter (PBS) that partially reflects and some passes, and a reflective mirror that is located between the PBS and the disk and that passes through the PBS onto the disk, and the beam reflected from the disk converts the path back to the PBS And an objective lens positioned between the reflective mirror and the disk to connect the beam reflected from the reflective mirror to the disk, and at the same time converting the beam reflected from the disk into parallel light, and positioned between the semiconductor laser and the collimating lens on the disk. A hologram that reflects and diffracts and focuses a P-polarized beam that has passed through the PBS and causes astigmatism, and by the hologram 6-segmented light detector for detecting focused signal and detecting error signal, and 2-segmented light for detecting information signal recorded by detecting part of S-polarized beam and P-polarized beam whose beam reflected from disk is split through PBS In particular, the optical disc comprises a Wollaston prism positioned between the PBS and the two-segment photodetector to separate the P and S waves, and a focusing lens for connecting the separated P and S waves to the two-segment photodetector. When the plane is defined as the x, y plane and the vertical direction of the optical disc as the Z axis, the active layer of the semiconductor laser is parallel to the xy-plane such that the polarization becomes P-polarized when the beam generated from the semiconductor laser is incident on the PBS. The hologram is composed of two semi-circular holograms, H ₁ and H ₂ , and the six-segment photodetector has two holes so that the two semi-circular beams connected by the two holograms maintain a constant distance from each other. By determining the position of the program, the distance between the two semi-circular beams on the six-segment photodetector can be achieved by configuring the six-segment line width.

According to the seventh embodiment of the present invention, the semiconductor laser 1, the hologram 12, the collimating lens 3 which makes the beam emitted from the semiconductor laser into parallel light, and the S-polarized beam reflect 100% as P7. A polarizing beam splitter (PBS, 4) for passing 50% of the polarized beam and reflecting 50%, a reflecting mirror (5) for bending the beam passing through the PBS in the direction of the disc, and on the disc The laser beam reflected by the reflecting mirror proceeds, and the beam reflected by the disk becomes parallel light again through the objective lens 6, passes through the reflecting mirror 5, and then enters the PBS 4. In the incident beam, 100% of the S-polarized beam and 50% of the P-polarized beam are reflected toward the Wollaston prism 17, passed through the Wollaston prism, and then split into two by the focusing lens 14 50% of the focused and P-polarized beams on (12) pass through the PBS (4) as it is and then focused by the collimator lens (3) Beams are formed the diffraction optical system so as to be connected on the six-segment photodetector (11) while passing through the hologram 12 to be.

In addition, the active layer of the semiconductor laser is configured to be parallel to the xy-plane such that the polarization becomes P-polarized light when a beam diverging from the semiconductor laser is incident on the PBS.

The hologram 2 is composed of two semicircular holograms H1 and H2 as shown in FIGS. 8, 9 and 10, and the positions of the reference lights of the two holograms are the light emitting points of the laser diodes, and the holograms H1 and H2. As shown in FIG. 9, the beam of the hologram H1 is focused at the position Q1 where the beam is circularly formed between the two focal points F1 and F2 such that the focal point in the YZ direction is F1 and F2, respectively, as shown in FIG. The beam by H2 is focused. Also, the beams focused by the holograms H1, H2 are separated by a distance d on the six-segmented light detector 11 as in the eighth, ninth, and tenth degrees, and this distance d is the PD1, It is equal to the line width of the dividing line that borders PD2, PD6 and PD3, PD4, and PD5.

The above-mentioned six-segment photodetector divides the size of the square into two equal parts by dividing the square in four directions in the diagonal direction as shown in FIG. 11 to make the Wollaston prism 17 a beam mixed with S and P waves as shown in FIG. When incident, two waves are separated while maintaining an angle.

The laser beam diverging from the semiconductor laser 1 generates the 0th and + 1-1th diffraction beams when passing through the hologram 12. Only the 0th diffraction beam passes through the hologram, and the 0th diffraction beam is a collimated lens. The light is converted into parallel light by (3), and only 50% is transmitted by the PBS. Then, the direction of travel is changed by the reflecting mirror 5 and focused on the disk by the objective lens 6. The beam focused on the disk is reflected on the disk and becomes parallel light again by the objective lens 6, and the parallel light passes through the reflecting mirror 5 and then enters the PBS 4, if information is recorded on the disk. If the S-wave component is included in the parallel light incident on the PBS and no information is recorded on the disc, the S-wave component does not exist.

Therefore, if information is recorded on the disk, the parallel light incident on the PBS contains S-wave components, so that the S-waves are reflected by 100% in the PBS, P-waves are passed by 50%, and 50% are reflected and reflected. 100% S-wave and 50% P-wave are mixed and incident toward the Wollaston prism (17), and only P-wave passing by 50% is incident to the collimator lens (3).

The mixed wave of the S and P waves incident on the Wollaston 17 is separated by a Wollaston prism at a constant angle as shown in FIG. 12 and connected to the two-segment photodetector 12 by the connection lens 14 to form a disk. If the information recorded on the disk is a magneto-optical signal (kerr rotation according to the magnetization direction), the signal difference between PD7 and PD8 of the two-segment photodetector 12, that is, the following equation (5) on

Optical information signal (opto-magnetic signal) = S7-S8 (Si: electrical signal of PDi)

Detected in the case of an uneven optical information signal signal recorded on a compact disc,

Optical information signal (pit signal) = S7 + S8

It is detected by the light quantity change as in the sixth formula. On the other hand, 50% of P-waves passing through PBS are used to detect focus errors and tracking errors. In more detail, after passing through the PBS, the P-wave is focused on the semiconductor laser emitting surface by the collimating lens 3, and the focused beam serves as a reference light of the hologram, and thus the holograms H1 and H2 as shown in FIG. Beams focused at the focal points F1 and F2 in the Y and Z directions, which are positions of the object light, are reproduced. When the six-segment photodetector 11 is installed at the positions Q1 and Q2 in which the beam is formed in a circle between these two connection points F1 and F2, the six-segment photodetector detects the reproduced beam as shown in the eighth, nineth, and tenth degrees. This generates the signals necessary to detect focus errors and tracking errors. That is, when the beam is focused on the hologram by the collimating lens 3 as described above, the focused beam is diffracted and focused on Q1 in the -Y direction of the six-segment photodetector 11 by the hologram H1, and by H2. When there is no focus error by diffraction focusing at each Q2 point in the + Y direction of the 6-segment photodetector, as shown in FIG. 11 (a), a beam is formed in a circular shape at the time of 6-segment photodetection, so that PD1, PD4, (PD2 + PD3), when the amount of light incident on (PD5 + PD6) becomes the same and the disk and the objective lens become closer, the beam is focused in the Z direction as shown in (b) of FIG. And the amount of light incident on PD4 becomes larger than the amount of light incident on (PD2 + PD3) and (PD5 + PD6), and conversely, when the distance between the disk and the objective lens is far away as shown in (c), the beam is focused in the Y-direction and Z The beam shape changes in the-direction so that the amount of light incident on (PD2 + PD3) and (PD5 + PD6) enters PD1 and PD4. It is larger than the amount of light.

Therefore, if the focal error signal FES is constructed as

Focus Error Signal (FES) = (S1 + S4)-(S2 + S3 + S5 + S5)

If no focus error occurs, FES = 0 and the focus error caused by the optical disk and the objective lens is closer to FES0, and the focus error caused by the optical disk and the objective lens farther from the lens becomes FES0.According to the FES signal, the actuator (actuator) By moving the objective lens up and down with (12), the focus error can be corrected.

Tracking error correction according to the present invention, since the boundary of the two-segment hologram is the same as the tangential direction of the disc track, the hologram H1 located inside the disc receives more light than the hologram H2 located outside the disc, so that PD1, PD2 and PD6 receive Since the beam intensity becomes greater than the beam intensity of PD3, PD4 and PD5, the tracking error signal system (TES) is expressed as shown in Equation 8 below.

Tracking Error Signal (TES) = (S1 + S2 + S6)-(S3 + S4 + S5)

If the focused beam is biased inside the track, it becomes TES0, and if the beam is biased outwards, the opposite phenomenon occurs and becomes TES0. Correct the tracking error. In this way, the optical pickup system according to the present invention can correct tracking errors and focus errors and read information recorded on the disc.

As described above, the optical pickup system that detects a signal by using a two-segmented hologram according to the present invention in a one-beam method using astigmatism and a push-pull method is a two-way optical pickup system. It is possible to accurately detect focus and tracking error signals without using a diffraction grating for beams, and to detect magneto-optical or pit signals recorded on a disc, thereby simplifying configuration and reducing manufacturing costs. It is effective to be able to

Claims (5)

A collimation lens for converting the light generated from the semiconductor laser into parallel light, and the S-polarized beam reflects a part of the totally reflected light and a part of the P-polarized beam out of the parallel light of the beam generated from the semiconductor laser and the beam reflected on the optical disk. A polarizing beam splitter (PBS), a reflection mirror that is located between the PBS and the disk and passes the beam through the PBS onto the disk, and the beam reflected from the disk converts the path back to the PBS, and the reflection mirror and the disk. An objective lens positioned between the focused mirror and a beam reflected from the reflective mirror to the disk, and at the same time the beam reflected from the disk is converted into parallel light, and positioned between the semiconductor laser and the collimating lens and reflected on the disk to pass through the PBS. A hologram that diffracts and focuses the P-polarized beam and causes astigmatism, and detects a beam focused by the hologram A six-segment photodetector for detecting the LR signal, a two-segment photodetector for detecting a portion of the S-polarized beam and the P-polarized beam whose beams reflected from the disk are split through the PBS, and detecting the recorded information signal; An optical pickup system comprising: a Wollaston prism positioned between two split light detectors to separate P and S waves; and a focused lens for focusing the separated P and S waves onto a two split light detector. The optical layer according to claim 1, wherein when the optical disk plane is defined as x, y planes, and the upper vertical direction of the optical disc as Z-axis, the active layer of the semiconductor laser is characterized in that P-polarized light is generated when a beam emitted from the laser is incident on the PBS. Wherein the active layer of the semiconductor laser is configured to be parallel to the xy-plane. The optical pickup system of claim 1, wherein the hologram comprises two holograms H ₁ and H ₂ that are semicircular. The optical pickup system of claim 1, wherein the six-segment photodetector determines the positions of the holograms so that the two semicircular beams focused by the two holograms maintain a predetermined distance from each other. The optical pickup system of claim 1, wherein the distance between the two semicircular beams on the six-segment photodetector is equal to the six-segment line width.